In lithography, there is an ongoing desire to reduce the size of features in a lithographic pattern in order to increase the density of features on a given substrate area. In photolithography, the push for smaller features has resulted in the development of technologies such as immersion lithography and extreme ultraviolet (EUV) lithography, which are however rather costly.
A potentially less costly road to smaller features (e.g. nanometer sized features, e.g., less than or equal to 50 nm, less than or equal 25 nm or less than or equal to 10 nm sized features) that has gained increasing interest is so-called imprint lithography, which generally involves the use of a “stamp” (often referred to as an imprint lithography template or an imprint lithography template) to transfer a pattern onto a substrate. An advantage of imprint lithography is that the resolution of the features is not limited by, for example, the emission wavelength of a radiation source or the numerical aperture of a projection system. Instead, the resolution is mainly limited to the pattern density on the imprint lithography template.
Imprint lithography involves the patterning of an imprintable medium on a surface of a substrate to be patterned. The patterning may involve bringing together a patterned surface of an imprint lithography template and a layer of imprintable medium (e.g., moving the imprint lithography template toward the imprintable medium, or moving the imprintable medium toward the imprint lithography template, or both) such that the imprintable medium flows around and about protrusions on the patterned surface, to adopt the topography of that patterned surface. Typically, the imprintable medium is flowable when the patterned surface and the imprintable medium are brought together. Following patterning of the imprintable medium, the imprintable medium is suitably brought into a non-flowable or frozen state (i.e. a fixed state), for example by illuminating the imprintable medium with actinic radiation. The patterned surface of the imprint lithography template and the patterned imprintable medium are then separated. The substrate and patterned imprintable medium are then typically processed further in order to pattern or further pattern the substrate. The imprintable medium may be provided in the form of droplets on the surface of a substrate to be patterned, but may alternatively be provided using spin coating or the like.
When the imprint lithography template is in contact with a layer of imprintable medium, the imprintable medium does not instantaneously flow around protrusions of the imprint lithography template to adopt the topography of the imprint lithography template. Instead, this process (often referred to as the squeezing or squeeze process), can take a prolonged period of time (known as the squeeze or squeezing time), relative to other parts of the imprint lithography process such as the deposition of the imprintable medium, or the fixing of a pattern imprinted in that medium. The prolonged time required to undertake the squeezing process results in a reduction of the throughput of an imprint lithography process, and thus perhaps forms a barrier to commercial wide-scale use of imprint lithography.